1. Field of Invention
The invention relates to a hydraulic control circuit for a work machine.
2. Description of Related Art
Work machines have a working portion that can be offset so as to swing laterally. In such work machines, there is a fear that a corresponding working portion may be brought into collision with the operator""s cab when the working portion moves. In these cases, measures should be taken to avoid collision or contact between the working portion and the operator""s cab.
Therefore, some work machines are provided with a position detecting means to detect the position of a working portion, and a control unit which is in charge of judging, on the basis of detection signals from the corresponding position detecting means, whether or not the working portion approaches the operator""s cab beyond an appointed range, wherein if it is judged that the working portion approaches the operator""s cab within the appointed range, a control command is issued from the control unit to a hydraulic circuit of a hydraulic actuator for the working portion, thereby stopping the movement of the working portion.
Such a work machine is shown in FIG. 8. However the electromagnetic proportional pressure reducing valves 57A and 57B, which operate based on commands from the control unit, are provided between a pilot type control valve 55, which controls feeding of pressurized oil to a hydraulic actuator 54 for a boom cylinder, and pilot valves 56A and 56B, which outputs pilot pressurized oil based on the operation of an operation lever. When the working portion is apart from the operator""s cab, the electromagnetic proportional pressure reducing valves 57A and 57B are opened to allow pilot pressurized oil to be supplied to the control valve 55. However, when the working portion approaches the operator""s cab, the electromagnetic proportional pressure reducing valves 57A and 57B are closed to shut off the pilot pressurized oil to the control valve 55, whereby the working portion is caused to stop. Thus, working efficiency is lowered when the working portion stops while the work machine operates.
Further, where work is carried out at places where underground electric wires exist or other underground obstacles reside, it is preferable to have a control means that prevents the working portion from being brought into contact with these obstacles. However, if such a control means is incorporated in a hydraulic control circuit of the working portion in addition to an interference prevention controlling means with respect to the abovementioned working portion and the operators cab, the circuit can be complex.
In various exemplary embodiments of a hydraulic control circuit for a work machine, the hydraulic control circuit includes a plurality of hydraulic actuators to actuate the working portion, and control valves that control feeding of pressurized oil to the respective hydraulic actuators, the hydraulic control circuit includes a valve driver to actuate the control valves on the basis of control commands from the control unit in the corresponding hydraulic control circuit, a control unit that determines whether or not the working portion has reached the predetermined interference prevention area and the limit position on the basis of input signals from a position detector which detects the position of the working portion, an interference prevention controller that, when it is judged by the corresponding determiner that the working portion has reached the interference prevention area, outputs control commands to the valve driver to stop the hydraulic actuators or to actuate the hydraulic actuators in a direction by which the working portion moves away from the work machine, and a position limitation controller that outputs control commands to stop the hydraulic actuators to the valve driver when it is judged by the determiner that the working portion has reached the limit position.
In another exemplary embodiment, the hydraulic control circuit for a work machines with a plurality of hydraulic actuators to actuate the working portion and control valves to control the feeding of pressurized oil to the respective hydraulic actuators, includes a valve driver to actuate the control valves on the basis of control commands from the control unit, and at the same time, the work machine is provided with, in the control unit, a determiner that determines whether or not the working portion has reached the predetermined interference prevention area with respect to the work machine body on the basis of input signals from the position detector to detect the position of the working portion, and an interference prevention controller that, when it is judged by the corresponding determiner that the working portion has reached the interference prevention area, outputs control commands to the valve driver to stop the hydraulic actuators or to actuate the hydraulic actuators in the direction by which the working portion moves away from the work machine wherein when the position limitation controller for outputting control commands to stop the corresponding hydraulic actuator in a case where the hydrauic actuators reach the limit position established separately from the abovementioned interference prevention area in the corresponding work machine, the determiner judges whether the hydraulic actuators reach the limit position, and a stop controlling command of the hydraulic actuators outputted from the position limitation controller is outputted to the valve driver which receives an output controlling command from the abovementioned interference prevention controller to stop the hydraulic actuators.
As such, the valve driving means may be constructed of a valve means which respectively carry out feeding and shut-off of pilot pressurized oil to the respective control valves on the basis of control commands from the control unit.
Also, in a work machine provided with hydraulic cylinders for booms which are swingable vertically and laterally with respect to the machine body as hydraulic cylinders, and hydraulic cylinders for sticks which actuates the sticks swingably connected to the tip end portion of the booms, such a work machine is provided with a interference prevention controller where the mechanism can continue a boom actuation while avoiding invasion by the working portion into the interference preventing area. The work machine can accomplish this by actuating the stick in a direction away from the interference prevention area when it is judged that at least while the boom is operating, the working portion has reached the interference preventing area, whereby it is possible to continue the operation while avoiding invasion by the working portion into the interference preventing area, and thus improve working efficiency.